A Study Of Segregated Pressure-based Algorithm And Simulations Of Cracking And Hydration Tubular Reactors

Tubular reactor is one of the most commonly used industrial chemical reactor types. Study of the physical processes occurring inside the reactor such as the fluid flow, heat transfer, mass transfer and chemical reactions is an important part of the reactor design. In recent years, with the development of computer technics and scientific computing, numerical simulation has become one of the most powerful tools to carry out such studies. Since the flow phenomenon inside the tubular reactor can be considered as incompressible in most of the cases, thus numerical simulation of the tube reactor is essentially solving each of the governing equations of flow.The segregated pressure-based algorithm is one of the most efficient and the most widely used methods for solving the incompressible Navier-Stokes equations. Two specific forms of this algorithm are the most famous which include the pressure correction method(such as SIMPLE algorithm) and fractional-step method(such as Projection algorithm). In this thesis, studies of these two algorithms have been carried out focusing on some of the existing problems to facilitate the methodological improvement and application. From the object-oriented programming concept, this thesis has developed a computer program for the SIMPLE algorithm with unstructured triangle meshes. This program has been validated by several classic benchmark numerical examples and provides a computing platform for further research and chemical applications. In addition, this thesis has studied the boundary conditions of the normal intermediate velocity of the pressure-free projection algorithm and investigated its impacts on the computational precision, which is conductive to the theoretical perfection and practical application.The thesis also studied the block correction technique which usually used to accelerate the iterative solution of the discrete equations and investigated its numerical characteristics in the case of tubular reactor simulation. It can be found from the study that when the ADI-TDMA algorithm is used combing with the block correction technique for solving discrete equations can significantly improve the transfer speed of the boundary conditions to the center of the reactor, and thus plays a role in accelerating the iteration convergence. Moreover, because of the geometrical distinction of the tubular reactor, axial block correction does not work, on the contrary, radial block correction accelerates the process of global convergence of the nonlinear system and this effect is completely reflected by accelerating pressure correction equation.Additionally, the SIMPLE algorithm with variables arranging on staggered grid has been adopted to simulate the non-catalytic hydration of ethylene oxide reactor and ethane cracking furnace tubes under the two-dimensional axisymmetric cylindrical coordinate. The governing equations have been discretized with the finite volume method. In order to obtain at least second-order accuracy, the convection terms and the diffusion terms have been treated with QUICK scheme and central difference scheme respectively. Source terms of the energy equation and component transportation equation have been calculated according to the relevant kinetic models provided by literatures. The k-ε model has been used for simulation of turbulent flow and wall functions have been employed for near-wall treatment. Results produced by numerical simulation have been proved good agreement with experimental and industrial data provided by the literature. In addition, it has been found from the simulation of ethane cracking tube that block correction technique causes pressure fluctuations and eventually leads to iterative divergence. To cope with this problem, some proper strategy should be used for solving the equation of state, so that the iteration process could be accelerated and reach convergence.